The present invention relates to a novel process for the continuous manufacture in an aqueous medium of fibrous material sheets--and particularly of paper--containing latex and optionally phenoplasts or aminoplasts, and to sheets obtained by means of this process as well as their possible re-use.
The world requirement as regards special papers is increasing. This is particularly true for water resistant papers intended for the manufacture of abrasives, adhesives, artificial leathers, etc. It is principally polymeric materials which confer on these special papers their impermeability, their flexibility and their resistance, and it is principally the phenoplasts or aminoplasts which permit different appropriate coatings to be laid which the manufacture of these different special papers requires.
To produce these different special papers, the conventionally used procedure is generally as follows:
the continuous sheet of fibrous material is wound normally during production thereof on a mandrel so as to form a reel. PA1 the reel obtained is then fed in a continuous length through another machine in one, two, three--or even more--passes, the purpose of which is to deposit on one or both faces of the fibrous material sheet different layers (latex, resins, etc.). PA1 adjustment of the pH between 4 and 5.5, and preferably between 4 and 4.5, PA1 addition of an electrolyte bridging agent the polarity of which is of the opposite sign to that of the latex to be used, whereby the electrolyte becomes attracted to and coats the surfaces of the fibres, PA1 addition of a foam inhibitor, PA1 re-adjustment of the pH between 4 and 5.5, if necessary, PA1 addition, preferably by injection, of the latex, which becomes attracted to and coats the electrolyte on the surface of the fibres, PA1 second addition of electrolyte (having the same characteristics as indicated above), PA1 possibly addition of resins (phenoplasts or aminoplasts), and PA1 re-adjustment of the pH to the previously indicated values, if necessary. PA1 starches (solubilized or insolubilized), PA1 carboxymethylcelluloses (solubilized or insolubilized), PA1 acrylic suspensions of all kinds, PA1 polyvinyl alcohols (solubilized or insolubilized), PA1 barrier solutions to organic solvents, PA1 natural or synthetic sizing agents, PA1 bonding products, etc. PA1 deposition on a face of the base of an anti-adhesive layer allowing the subsequent winding into a reel and unwinding of the finished product for use, PA1 deposition on the other face of the initial base and, in another machine, of an adhesive layer.
It is only then that the sheet, after appropriate drying, is again wound in a reel. That is to say that in order to obtain the desired paper, it is necessary to repeat the winding and unwinding operations a plurality of times, applying each time a new coat. That obviously considerably increases the cost price of a reel. It has not been possible up to present to operate in a single pass (e.g. by mixing the pulp--crude or refined--with latex) to obtain directly the desired paper. This is perhaps due to the presence of coagulated beads and deposits of latex (or resins) in the circuit using the mixture or in the machine manufacturing the sheet, which phenomena make rapidly impossible any continuous manufacture. This may be also due to the very poor retention of the latex and the resins on the fibrous material. Nevertheless, despite the evidence of a spectacular lowering of the cost price if the latex (or other additives) could be added into the body of the pulp in the papermaking machine, this simplification of manufacture has never yet been successfully implemented and recourse is always had to a plurality of long and costly passes.
The present invention has consequently as its aim to provide a new process for the continuous manufacture of fibrous materials containing an impermeabilizing agent such as latex, which answers better the requirements of practice than the previously known processes having the same aim, more especially in that it allows not only a whole series of coating steps to be left out by manufacturing the paper from fibrous materials containing latex in their mass but also a perfectly homogeneous paper to be obtained--more homogeneous and more even that that obtained by the previously known processes.